1. Field of the Invention
The invention is in the field of high-strength film laminates. The laminates of the invention have layers of plasticizer-containing polyvinyl (n)acetal and plasticizer-containing polyvinyl (iso)acetal
2. Background Art
The invention relates to a film laminate, for example suitable as an intermediate layer in laminated safety glazings, the film laminate being formed from at least three layers of plasticizer-containing polyvinyl (n)acetals and/or polyvinyl (iso)acetals, and having good penetration properties.
Laminate safety glazings generally consist of two glass panes and an intermediate film connecting the glass panes. Plasticizer-containing polyvinyl butyral (PVB) is predominantly used as the film material and is obtainable by reacting polyvinyl alcohol with n-butyraldehyde.
An increasingly important feature of safety glazings is the penetration strength thereof, that is to say the resistance thereof to the effect of external force. The penetration force can be augmented by a thicker glass pane, and also by correspondingly thicker intermediate-layer films. For example “hurricane-proof” glazings are thus known, which offer improved protection against flying objects. To this end, relatively thick standard films made of PVB are generally used, which, however, reduces the transparency of the glazing. In addition, a relatively thick glazing is undesirable due to the limited installation depth and the relatively high costs.
Furthermore, relatively mechanically stable films, for example made of PET or PU, can be laminated between two PVB films to improve the penetration strength of safety glazings. However, this involves an additional processing step and poses the risk of undesired delamination.
In general, the mechanical strength of PVB films can be adjusted by the plasticizer content thereof or by the proportion of polyvinyl alcohol groups or polyvinyl acetate groups in the polyvinyl acetal. For example, U.S. Pat. No. 5,340,654 or WO 2006/102049 describe multi-layer systems in which a first layer contains a polyvinyl butyral having a high residual acetate content and a second layer contains a polyvinyl butyral having a low residual acetate content. Similarly, WO 2008/137367 describes multi-layer systems in which the sub-layers made of polyvinyl butyral differ in terms of their polyvinyl alcohol content.
Due to the different residual acetate contents and different proportions of polyvinyl alcohol groups, the sub-layers have a different plasticizer content and therefore different mechanical strength. Mechanical decoupling and therefore improved soundproofing are thus achieved.
The known multi-layer films are based on polyvinyl butyral, which is obtainable by reacting polyvinyl alcohol with n-butyraldehyde. Different plasticizer contents of the layers, which can be assimilated in part by migration, are obtained with use of polyvinyl butyrals having different polyvinyl alcohol or polyvinyl acetate contents. Plasticizer migration can also lead to incompatibilities with the polymer matrix and therefore to plasticizer exudation. The mechanical properties of the films, such as tensile strength or tear strength, likewise are highly dependent on plasticizer content. The mechanical properties of the film generally worsen with an increase in plasticizer content and with a decreasing number of polyvinyl alcohol groups of the polyvinyl butyral used.